a b s t r a c tIn this study, the interfacial reactions on Sn, Sn-3.0Ag-0.5Cu, Sn-0.7Cu, Sn-58Bi and Sn-9Zn lead-free solders with the Au/Pd/Ni/Cu multilayer substrate at 240-270 • C for 20 min to 20 h were investigated. The experimental results showed that the (Ni, Cu) 3 Sn 4 phase is converted to the (Cu, Ni) 6 Sn 5 and Cu 3 Sn phases in the Sn/Au/Pd/Ni/Cu system when the reaction time is longer than 4 h. In Sn-3.0Ag-0.5Cu/Au/Pd/Ni/Cu and Sn-0.7Cu/Au/Pd/Ni/Cu systems, the (Cu, Ni) 6 Sn 5 and Cu 3 Sn phase were observed, and only the Ni 3 Sn 4 phase was formed at the Sn-58Bi/Au/Pd/Ni/Cu interface. Furthermore, the Pd 2 Zn 9 and NiZn phases were formed in the Sn-9Zn/Au/Pd/Ni/Cu system. When the reaction time was longer than 4 h, the Pd 2 Zn 9 , NiZn, and Ni 5 Zn 21 phases were formed at the interface. The reaction mechanism for all the reaction systems was diffusion-controlled. The Sn-58Bi/Au/Pd/Ni/Cu system was found to have the lowest activation energy when compared with other systems, and its value was 17.43 kJ/mol.

Thick and smooth amorphous Si film of 2 µm without hillocks has been obtained at low temperature of 300 °C by plasma-enhanced chemical vapor deposition (PECVD) technology. In comparison with conventional sputtering deposition, PECVD-deposited thick amorphous Si film has better adhesion to Si or oxide substrate without cracking or peeling. The film quality depends on the following process parameters: RF power, frequency mode and gas flow ratio as well as substrate material. The deposition rate increases with the RF power for both RF modes of 380 kHz and 13.56 MHz, and higher deposition rate together with lower compressive stress occurs at high frequencies of 13.56 MHz. Amorphous Si film without hillocks is formed on the 100 nm oxide/Si(100) substrate while some hillocks appear on the top of the amorphous Si film deposited on the crystalline Si(100) substrate. Good quality of amorphous Si at low temperature is very important for the fabrication of MEMS devices. Fabrication of suspended MEMS microstructure and sensor array has been demonstrated using the smooth amorphous Si films as sacrificial layer in surface micromachining.

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NbN x films were prepared by RF reactive magnetron sputtering from a Nb target in N 2 / Ar gas mixtures and then used as diffusion barriers between Cu and Si substrates. Material characteristics of the NbN x, films were investigated and were correlated with the N 2 /Ar flow ratio. The variations in film resistivity is correlated with the change of phases and chemical compositions from α-Nb, β-Nb 2 N, γ-Nb 4 N 3 , δ-NbN + δ -NbN as the N 2 /Ar ratio is increased. The thermal stability of Cu (60 nm)/NbN x (25 nm)/Si multilayers were investigated and our results indicated that the barrier performances were significantly affected by the chemical composition of NbN x films. The diffusion coefficient of Cu in NbN x was measured by four-point probe analysis after annealing Cu/NbN x /Si multilayered samples in the temperature range of 600-850 • C. Cu diffusion in NbN x had components from the grain boundaries and the lattice. In addition, our results suggest that the NbN x can be used as a potential diffusion barrier for Cu metallization as compared to the conventional TaN.Metallization technologies become increasingly important for advanced ultra-large scale integration (ULSI) devices as geometry shrinks and complexity increases. Copper has replaced aluminum and its alloys as the interconnect metal for deep submicron ULSI circuits because of its lower bulk resistivity (1.67 μ cm) and higher resistance to electromigration and stress voiding. 1 However, Cu reacts with Si at relatively low temperatures, leading to device leakage. Therefore, it has been widely adopted to insert a diffusion barrier to suppress Cu diffusion and the subsequent reaction with Si for silicon integrated circuit applications. 2 Of the various diffusion barrier candidates, tantalum nitride (TaN) is considered as a promising material and has been widely used as the diffusion barrier for Cu metallization because of its high thermal stability and the absence of any compounds between Cu and Ta, and Cu and N. 3-5 However, TaN barrier layer needs to be further improved or be replaced with other materials because of the three issues associated with the shrinkage of Cu lines. One is the high resistivity of TaN, which increases the total resistivity of interconnects when the width of wire shrinks furthermore. The second issue is the high interface energy of Cu/TaN, which causes poor adhesion of Cu and enhances the electro-migration failure. 6 The third issue is the poor step coverage of thick or multiple TaN-based layers. The continuous demands to scale down devices require that the thickness of Cu diffusion barriers should be significantly reduced for advanced nano-meter level halfpitch application. Hence, a thin, excellent conformal diffusion barrier is required.In addition to TaN, many nitrides have been extensively studied for applications in microelectronics, such as binary TiN 7 and WN, 8 ternary Ti-Si-N, One of new barrier nitrides, NbN, deposited by using atomic layer deposition (ALD) with precursors of NbCl 5 and NH 3 , 24 exhibited good thermal sta...

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